<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>兄弟选择器</title>
    <style>
        h1,
        p {
            font-size: 24px;
        }

        .brother1,
        #brother2 {
            color: chartreuse;
        }
    </style>
</head>
<body>
    <h1 class="brother1">兄弟</h1>
    <p id="brother2">兄弟选择器</p> 
</body>
</html>